The present invention relates to an ultraviolet irradiating device and related method, and more particularly to an apparatus for a photo-alignment process in which the UV light is uniformly and widely irradiated into the alignment layer to obtain a large size liquid crystal display.
A conventionally used liquid crystal display is mainly a twisted nematic liquid crystal display (referred as TNLCD), which has a changeable transmittance at each gray level according to the viewing angle. In particular, while the transmittance is symmetrical in the horizontal direction, the transmittance is asymmetrical in the vertical direction. Therefore, in the vertical direction, a range with an inverted image phenomenon occurs so that the vertical viewing angle becomes very limited.
To overcome this problem, a multi-domain liquid crystal cell, in which a pixel is divided into more than two pretilts where the pretilt defines pretilt angle and pretilt direction, is introduced.
However, manufacturing the multi-domain liquid crystal cell by the conventional method, a reverse rubbing method, is too complicated because it comprises the following steps: rubbing the entire alignment layer in a first rubbing direction; applying a photoresist as a mask for blocking one domain; rubbing the other domain in a reverse direction to the first rubbing direction; and removing the photoresist. Using a reverse rubbing process generates dust and/or an electrostatic discharge, thus reducing productivity and/or damaging the thin film transistor which drives a pixel. In addition, to eliminate an image inversion phenomenon completely, each pixel is divided into more than 4 domains. However, it is exceedingly difficult to fabricate a 4-domain liquid crystal cell by this reverse rubbing technique.
As another alignment method, a photo-alignment method is used. In this method, since the pretilt, defining a pretilt angle and a pretilt angle direction, is determined on the alignment layer by irradiating UV light instead of a rubbing process, the fabricating process is simple and the damage to the substrate can be prevented. By irradiating light into the alignment layer, which includes a photopolymer, the photopolymer is photopolymerized by the cross linking generated between the polymers. Therefore, a pretilt on the alignment layer is determined according to the direction and the degree of cross linking of the photopolymers; the cross linking depending on the polarization direction, the incident direction of the light, and the amount of photo-energy of the light absorbed into the alignment layer. In other words, the direction and the magnitude of the pretilt are determined according to the polarization direction of the UV light and the photo-energy absorbed into the alignment layer. Indeed, to make a multi-domain liquid crystal cell, each domain is respectively exposed to UV light having a different polarization direction and a different photo-energy. Therefore, it is important to conform the uniformity of photo-energy absorbed into the alignment layer as well as the size of the spot of the light to make a large size liquid crystal display.
FIG. 1 is a view showing the conventional UV light irradiating apparatus. In FIG. 1, the UV light generated from a UV lamp 1 is focused by a lens 2 and then linearly polarized by a polarizer 3. These elements are arranged in a line with a substrate 4. The substrate 4, coated with an alignment layer 5 that can be photo-reacted, is exposed by the circular spot of the UV light, so that a pretilt is given to the alignment layer 5 formed on the substrate 4.
Irradiating UV light to the alignment layer 5 by the conventional UV irradiating apparatus, however, is limited by the size of the UV lamp 1, so the exposed circular area 6 on the alignment layer 5 is also small as shown in FIG. 2a. In addition, to get a uniform pretilt on the alignment layer 5, the available alignment layer size is smaller than the area corresponding the plateau of the graph of FIG. 2b having a uniform photo-energy. The available alignment layer size is restricted by the size of the lamp.
Accordingly, it is difficult to employ this UV irradiating apparatus for a large size liquid crystal display. In addition, there is a problem that the UV light cannot be uniformly irradiated into the entire alignment layer. As a result, the absorbed energy on the whole alignment layer is not uniform.